The glacial flooding that sent residents of Alaska's capital city scrambling this week has become an annual ordeal for those who live along the picturesque river that winds from the nearby Mendenhall Glacier.
This year, a giant wall of reinforced sandbags erected with the help of the U.S. Army Corps of Engineers held back the worst of the flooding in Juneau, to residents' great relief. The damage was nothing like what happened the last two years, when flooding was rampant and some homes washed away.
But the wall is merely a temporary barrier. The effort to devise a permanent solution is complicated by what scientists don't yet know about how human-caused global warming will impact the yearly outbursts of water from an ice dam at the glacier. Juneau is just one of many communities around the globe struggling to engineer a way out of the worst damage from climate change.
“We can’t keep doing this,” said Ann Wilkinson Lind, who lives on the banks of the Mendenhall River. “We need a levee or some other permanent fix. ... This is an emergency situation that can’t take 10 years for this study and that study and every other study. It needs to be done now.”
The Mendenhall Glacier is about 12 miles (19 kilometers) from Juneau, home to 30,000 people in southeast Alaska, and is a popular tourist attraction due to its proximity and easy access on walking trails. Homes on the city’s outskirts are within miles of Mendenhall Lake, which sits below the glacier, and many front the Mendenhall River.
The glacial outburst flooding from the Mendenhall is itself a phenomenon caused by climate change, which is thinning glaciers around the world. A glacier nearby retreated, leaving behind a large bowl — Suicide Basin — that fills each spring and summer with rainwater and snowmelt dammed by the Mendenhall.
When that water builds up enough pressure, it forces its way under or around the ice dam, enters Mendenhall Lake, and flows down the Mendenhall River toward Juneau. Flooding from the basin has been an annual concern since 2011 and has gotten worse, with new water-level records being set each of the last three years.
City officials responded this year by working with state, federal and tribal entities to install the temporary barrier along roughly 2.5 miles (4 kilometers) of riverbank. The 10,000 “Hesco” barriers are essentially giant, reinforced sandbags intended to protect more than 460 properties, said emergency manager Ryan O’Shaughnessy.
The Juneau Assembly required homeowners in the flood zone to cover 40% of the barrier's cost — about $6,300 each over 10 years. Additionally, a handful of homeowners were asked to chip in $50,000 toward reinforcing the river bank. About one-quarter of the residents formally objected, not enough to torpedo the project.
This week, some water seeped between the bastions or through pipes underneath them that are designed to allow water to drain from yards into the river. Valves in the pipes are supposed to prevent floodwater from entering. But officials uniformly called the project a success, while acknowledging that some homes were damaged and that the barrier needs to be further extended.
The barriers are designed to last for up to 10 years to allow time for a long-term solution. But questions abound.
The capacity of Suicide Basin seems to be growing, and scientists aren't sure what a worst-case flood might look like. They predict that within a few decades, the Mendenhall itself will retreat far enough that it no longer acts as a dam, eliminating the risk of a flood outburst from Suicide Basin. But the persistent melting could also form other glacially dammed lakes that could function in a similar way.
“There’s still a lot to be learned,” said Nate Ramsey, Juneau's engineering and public works deputy director. “We have to assume this will be an annual event for the next many, many years. Is something like a temporary, soil-filled basket levy the best we can do over that period of time? ... We’ve got to keep looking for a long-term solution.”
The Army Corps of Engineers has nearly $5 million set aside to begin working on a long-term solution, which for now largely consists of data collection.
“It’s like trying to solve a math problem when the variables are always changing,” Army Corps Brig. Gen. Clete Goetz said Thursday. “Seeing the problem is not the hard part. Engineering the solution is the challenge. That’s what we’re here for.”
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Johnson and Attanasio reported from Seattle. Rush reported from Portland, Oregon.
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